Bug 303078 – [appearance: base] Add -internal-auto-base() and resolve it by substitution

• Status: RESOLVED
• Resolution: FIXED
• Component: Forms

[Said Abou-Hallawa]

To add support for `appearance: base` a new internal function `-internal-auto-base()` is added. This functional will resolve and substitute itself with one of two values depending on whether the style has `appearance: base` or not.

For example, this CSS defines the border style of the radio button if it has `appearance: base`. Otherwise its value is unset.

input[type=radio] {
    border-radius: -internal-auto-base(unset, 100%);
    border: -internal-auto-base(unset, 0.4em solid currentColor);
}

[Radar WebKit Bug Importer]

<rdar://problem/165381349>

[Said Abou-Hallawa]

Pull request: https://github.com/WebKit/WebKit/pull/54435

[EWS]

Committed 303693@main (04ea7c36cab8): <https://commits.webkit.org/303693@main>

Reviewed commits have been landed. Closing PR #54435 and removing active labels.